Total parenteral nutrition has allowed the critically ill, burned patient full metabolic and nutritional support. The role lipids play in this resuscitative effort crucial. It is known that long chain fatty acids, as a fuel source, are not effective in sparing protein catabolism in the burn patient. Carbohydrate is needed in an amount equal to the basal energy expenditure to decrease protein catabolism and gluconeogenesis and, therefore, improve nitrogen balance. Beyond the basal energy expenditure, carbohydrate and lipid serve as equivalent nitrogen-sparing energy sources. However, an altered metabolism occurs during a stress such as a burn, where there is increased oxidation of branched chain amino acids in skeletal muscle, inhibition of ketogenesis from long chain fatty acids and enhanced lipogenesis and defective plasma lipid disposal. Medium chain length fatty acids are uniquely oxidized during stress and are also ketogenic and will potentially improve the negative nitrogen balance. The ketone bodies will provide an alternate substrate for muscle energy requirements and will, therefore, allow for increased amino acid anabolism into acute phase proteins and maintenance of the host immune response and, ultimately, survival. We will conduct experiments, using a thermal injury rat model, to discern the benefits of medium chain fatty acids in terms of nitrogen balance, protein turnover studies and immune function.